I know I could just go buy a mag-mount mobile antenna, but would it be
possible or even practical to build a J-pole type or vertical (without long
radials) antenna for 2m/70cm, out of welding rod, which could be small
enough to be easily portable and used inside different rooms? Our local
RACES is trying to set up a volunteer communications network inside several
different city and county offices to assist in emergencies. I have searched
(a little) for such a design, and found something similar, made out of TV
line, but would prefer something that could be made free standing and as
small as practical. The Welding Rod antennas made with 45 degree radials
are a little bulky to move through congested hallways. The idea is to make
it portable enough to move from room to room as needed. Long radials would
impede moving through hallways.
Thanks in advance, KE5GEO

Chuck James wrote:
I know I could just go buy a mag-mount mobile antenna, but would it be
possible or even practical to build a J-pole type or vertical (without long
radials) antenna for 2m/70cm, out of welding rod, which could be small
enough to be easily portable and used inside different rooms? Our local
RACES is trying to set up a volunteer communications network inside several
different city and county offices to assist in emergencies. I have searched
(a little) for such a design, and found something similar, made out of TV
line, but would prefer something that could be made free standing and as
small as practical. The Welding Rod antennas made with 45 degree radials
are a little bulky to move through congested hallways. The idea is to make
it portable enough to move from room to room as needed. Long radials would
impede moving through hallways.
Thanks in advance, KE5GEO



There are mny plans available on the Internet for free standing
J-poles made out of 1/2 -3/4 inch copper tubing.

Good luck, jimbo

On Thu, 28 Dec 2006 10:03:31 GMT, "Chuck James"
wrote:

I know I could just go buy a mag-mount mobile antenna, but would it be
possible or even practical to build a J-pole type or vertical (without long
radials) antenna for 2m/70cm, out of welding rod, which could be small
enough to be easily portable and used inside different rooms? Our local
RACES is trying to set up a volunteer communications network inside several
different city and county offices to assist in emergencies. I have searched
(a little) for such a design, and found something similar, made out of TV
line, but would prefer something that could be made free standing and as
small as practical. The Welding Rod antennas made with 45 degree radials
are a little bulky to move through congested hallways. The idea is to make
it portable enough to move from room to room as needed. Long radials would
impede moving through hallways.
Thanks in advance, KE5GEO


You might get some design ideas looking at the j-poles at
http://www.arrowantennas.com/

I personally have a j-pole made from a small length of 450-ohm line,
which could be made self-supporting with a wood dowel and stand.

Lotta ways to do this...

bob
k5qwg

Chuck James wrote:
...


Why not just through together a 1/2~ monopole with a simple gamma match
and 1:1 current balun?

Regards,
JS

"Bob Miller" wrote in message
...
On Thu, 28 Dec 2006 10:03:31 GMT, "Chuck James"
wrote:

I know I could just go buy a mag-mount mobile antenna, but would it be
possible or even practical to build a J-pole type or vertical (without
long
radials) antenna for 2m/70cm, out of welding rod, which could be small
enough to be easily portable and used inside different rooms? Our local
RACES is trying to set up a volunteer communications network inside
several
different city and county offices to assist in emergencies. I have
searched
(a little) for such a design, and found something similar, made out of TV
line, but would prefer something that could be made free standing and as
small as practical. The Welding Rod antennas made with 45 degree radials
are a little bulky to move through congested hallways. The idea is to
make
it portable enough to move from room to room as needed. Long radials
would
impede moving through hallways.
Thanks in advance, KE5GEO


You might get some design ideas looking at the j-poles at
http://www.arrowantennas.com/

I personally have a j-pole made from a small length of 450-ohm line,
which could be made self-supporting with a wood dowel and stand.

Lotta ways to do this...

bob
k5qwg

Agree. I have made copper pipe j-poles for 50,144, 220 & 440 bands. They
match well; sometimes I can hit 1:1 at the sweet spot. They are virtually
indestructable and very cheap. Gonna do one for 10M next. (It'll be about
24 feet tall and will likely need guy ropes.)

Any instructions on just how to do that? I'm relatively new to this hobby.

"John Smith I" wrote in message
...
Chuck James wrote:
...

Why not just through together a 1/2~ monopole with a simple gamma match
and 1:1 current balun?

Regards,
JS

Chuck James wrote:
...

Chuck:

I have been tearing apart this place. About a year ago I had
constructed one for 10 meters and had all my notes, etc. Now can't find
a thing.

This link:
http://www.cebik.com/trans/gamma.html

will show you details of a gamma match. It is being used on a dipole
element. Basically, you just use the top half of the element, the half
with the gamma match. Just below the gamma match, you chuck in a 1:1
current balun to choke off the rf which might go to the outside of the coax.

A counterpoise of wire, cut to 1/2 wave at the center freq. of the band
can be attached to the outside of the coax (or coax connector) at the
antenna.

The monopole radiator is a simple 1/2 wave and the length can be
computed from the standard formula: 5904/(frequency in mhz) = length.

The link above contains a basic program to compute the gamma match
dimensions. You should be able to tear the formulas out of the text and
use them manually.

I will see if I can't find the material on dimensions, etc. I had put
together here, still looking.

Regards,
JS

You are not asking for the moon. What you want is a simple, compact,
reliable antenna for both 144 and 440 MHz.. Having done a fair amount of
that sort of RACES/ARES stuff, here's what I'd advise you.

Go down to your local radio parts store, Rat Shack if that's all you've got
and get yourself a female BNC chassis connector (UG-1094, RS # 278-105).
Get a couple of quality male BNC cable connectors while you are at it.
Unfortunately for you, RS doesn't sell anything but that twist-on solderless
crap for male BNC, so you may wind up buying them mail order.

Get yourself four 3/8" solder lugs and five 19" pieces of solid #14 copper
wire (strip house romex if you have to).

To each of the four solder lugs, solder one end of the #14 wire. These will
be the four ground plane wires. THe fifth piece of #14 will connect to the
solder cup on the bottom of the female BNC chassis connector to become the
radiating element.

Now put those four solder lugs over the radiating element and over the
threads on the connector. Use the nut that came with the connector to
fasten the solder lugs, each at approximately 90° from each other (a small
crescent wrench or dedicated 1/2" wrench needs to be part of your permanent
tool kit). Bend them down at about a 45° angle.

Take the two male connectors and make an RG-58 cable to run from your radio
to where you want to put your antenna. Connect one end of the cable to your
radio and the other end to the UG-1094 connector.

You want to move the antenna? Disconnect the cable. Grab your wrench and
pull that nut off. Take off all 4 ground plane wires. Bundle them up
around the radiating element. Reassemble in the new location. Ten seconds
up, ten seconds down.

You want to use it in the field outside? Bend a small hook (no more than
1/4" long) in the radiating element. Tie a roll of heavy twine to the hook
and bend the hook shut. Take the roll of twine and throw it around the
highest tree limb you can find. Hoist that sucker up and you are on the
air.

We can dick around with a mounting bracket on the UG-1094 threads if you
want to make a permanent installation out of it.

(By the way, you are operating close enough to the third harmonic of 144 on
440 that the antenna will perform quite well on both frequencies.)

Jim









"Chuck James" wrote in message
t...
I know I could just go buy a mag-mount mobile antenna, but would it be
possible or even practical to build a J-pole type or vertical (without long
radials) antenna for 2m/70cm, out of welding rod, which could be small
enough to be easily portable and used inside different rooms? Our local
RACES is trying to set up a volunteer communications network inside several
different city and county offices to assist in emergencies. I have
searched (a little) for such a design, and found something similar, made
out of TV line, but would prefer something that could be made free standing
and as small as practical. The Welding Rod antennas made with 45 degree
radials are a little bulky to move through congested hallways. The idea is
to make it portable enough to move from room to room as needed. Long
radials would impede moving through hallways.
Thanks in advance, KE5GEO

RST Engineering wrote:
(By the way, you are operating close enough to the third harmonic of 144 on
440 that the antenna will perform quite well on both frequencies.)

It will even perform well as a satellite antenna on
440. EZNEC says it has a TOA of about 45 degrees.
--
73, Cecil http://www.w5dxp.com

And I did not mean to imply that you couldn't use brazing (not welding) rod,
which is nothing but brass and a little more to make the elements. IT
certainly makes a STIFFER antenna, but copper wire is a lot easier to work
with.

Jim



"Cecil Moore" wrote in message
et...
RST Engineering wrote:
(By the way, you are operating close enough to the third harmonic of 144
on 440 that the antenna will perform quite well on both frequencies.)

It will even perform well as a satellite antenna on
440. EZNEC says it has a TOA of about 45 degrees.
--
73, Cecil http://www.w5dxp.com